:root {
  --azul: #0d47a1;
  --celeste: #4fc3f7;
  --blanco: #ffffff;
  --texto: #0f172a;
  --bg: #f8fafc;
  --gris: #eef3f7;
  --radius: 16px;
  --shadow: 0 8px 24px rgba(13, 71, 161, 0.12);
  --header-h: 72px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Noto Sans, Ubuntu, Cantarell, Arial, "Apple Color Emoji", "Segoe UI Emoji";
  color: var(--texto);
  background: var(--bg);
}
img { max-width: 100%; height: auto; display: block; }
a { color: inherit; text-decoration: none; }
.container { width: min(1100px, 92%); margin-inline: auto; }

.site-header {
  position: sticky; top: 0; z-index: 50;
  background: linear-gradient(90deg, var(--azul), var(--celeste));
  color: var(--blanco);
  box-shadow: var(--shadow);
}
.header-inner { display: flex; align-items: center; justify-content: space-between; height: var(--header-h); }
.brand { display: inline-flex; align-items: center; gap: 12px; margin: 0; font-weight: 800; letter-spacing: .3px; font-size: clamp(20px, 3.6vw, 36px); }
.brand span { color: #e3f2fd; font-weight: 900; }

.site-nav { display: flex; align-items: center; }
.nav-list { display: flex; gap: 8px; list-style: none; margin: 0; padding: 0; }
.nav-link { padding: 10px 14px; border-radius: 999px; transition: background-color .2s ease, color .2s ease, box-shadow .2s ease; color: var(--blanco); border: 1.5px solid rgba(255,255,255,.35); }
.nav-link:hover { background: rgba(255,255,255,0.15); box-shadow: 0 0 0 2px rgba(255,255,255,.25) inset; }
.nav-link.is-active { background: var(--blanco); color: var(--azul); border-color: transparent; }

.game-card { background: var(--blanco); border: 1px solid #e6eaf0; border-radius: var(--radius); padding: 24px; margin: 28px auto 40px; box-shadow: var(--shadow); }
.game-card h2 { margin: 0 0 6px; font-size: clamp(18px, 3.6vw, 28px); color: var(--azul); }
.subtitle { margin: 0 0 16px; color: #35506e; }

.controls { display: flex; flex-wrap: wrap; align-items: center; gap: 12px; margin: 6px 0 12px; }
.controls label { font-weight: 600; color: var(--azul); }
.controls select { padding: 10px 12px; border-radius: 12px; border: 2px solid #cfe3ff; background: #f6fbff; font-weight: 600; color: #083b86; }
.toggle { display: inline-flex; align-items: center; gap: 8px; }

.board { width: min(420px, 92vw); aspect-ratio: 1 / 1; margin: 10px auto 18px; display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; }
.cell { background: #f5f9ff; border: 2px solid #cfe3ff; border-radius: 12px; display: grid; place-items: center; font-size: clamp(36px, 10vw, 64px); font-weight: 800; cursor: pointer; user-select: none; transition: transform .06s ease, box-shadow .15s ease, background .2s ease, border-color .2s ease; }
.cell:hover { transform: translateY(-2px); box-shadow: 0 6px 16px rgba(3, 169, 244, 0.25); }
.cell.taken { background: #e9f2ff; border-color: #b8d5ff; cursor: default; }
.cell.x { color: var(--azul); }
.cell.o { color: var(--celeste); }
.cell.disabled { pointer-events: none; opacity: .7; }

.panel { display: flex; gap: 12px; justify-content: space-between; align-items: center; flex-wrap: wrap; }
.status { font-weight: 700; color: var(--azul); }

.btn {
  appearance: none;
  padding: 10px 14px; font-weight: 800; border-radius: 12px; cursor: pointer;
  background: var(--blanco);
  color: var(--azul);
  border: 2px solid var(--azul);
  box-shadow: 0 4px 12px rgba(3, 169, 244, 0.18);
  transition: background .18s ease, color .18s ease, transform .08s ease, box-shadow .18s ease, border-color .18s ease;
}
.btn:hover { background: #eef6ff; box-shadow: 0 6px 16px rgba(3, 169, 244, 0.25); }
.btn:active { transform: translateY(1px); }
.btn:focus-visible { outline: 0; box-shadow: 0 0 0 3px rgba(79,195,247,.35); }

.btn--fill { background: linear-gradient(180deg, var(--celeste), #7bd3ff); color: #083b86; border-color: #0b53c7; }
.btn--fill:hover { filter: brightness(.98); }

.site-footer { border-top: 1px solid #e2ebf5; padding: 18px 0 28px; text-align: center; color: #4d6b8a; }

@media (max-width: 640px) {
  :root { --header-h: 64px; }
  .game-card { padding: 16px; }
}